The present invention relates generally to the implantation of prosthetic devices, and more particularly to a method and apparatus for preparing a bone for receiving a prosthetic device.
The hyaline articular cartilage of a natural knee joint may undergo degenerative changes due to various etiologies. When these degenerative changes are advanced, it may ultimately become necessary to replace the natural knee joint with an artificial knee joint prosthesis. A knee joint prosthesis typically comprises a femoral component and a tibial component. The femoral component and tibial component are designed to be surgically attached to the distal end of the femur and proximal end of the tibia respectively. After being surgically attached, the femoral component is able to engage the tibial component in such a manner as to simulate the articulating motion of an anatomical knee joint.
When preparing the femur and tibia for receiving a knee joint prosthesis, it is important that the components of the knee joint prosthesis be properly positioned on the femur and tibia to minimize the possibility that complications may result. To facilitate proper positioning of the femoral component of the knee joint prosthesis, the orientation of the intramedullary canal of the femur is often used as a reference point when determining the manner in which the distal femoral surface should be shaped. In this regard, it is a common practice to prepare an anterior-posterior radiograph of the femur prior to surgery. The angle of the intramedullary canal of the femur relative to the vertical axis of the body (i.e., the valgus angle of the femur) is then determined. An intramedullary rod is then inserted into the intramedullary canal of the femur. The intramedullary rod generally includes an angled portion which is angularly displaced from the main portion of the rod by an angle equivalent to the valgus angle. The angled portion of the intramedullary rod is then used to orient various shaping instruments which are used when the distal femoral surface is resected. In this regard, several different cutting guides and a planer may be secured to the angled portion of the intramedullary rod to ensure that the shape of the resected femur reflects the valgus angle of the femur.
While the method described above is effective in shaping the distal end of the femur to receive the femoral component of a knee joint prosthesis, there are nevertheless several disadvantages associated with using this method. For example, because the intramedullary rod generally includes an angled portion, the intramedullary rod is often relatively difficult to insert into the intramedullary canal. This is because it is generally difficult to impact the angled portion of the intramedullary rod in a direction which is displaced from the axial centerline of the angled portion. A further disadvantage of the method described above is that a complete set of surgical instruments for implanting a knee joint prosthesis must generally include a number of different intramedullary rods having different angled portions, one for each possible range of valgus angles. This is complicated by the fact that shorter intramedullary rods may sometimes be necessary when an existing hip implant is present, thereby increasing the number of intramedullary rods which are necessary to form a complete set of instruments. While a planer which is operable to engage a straight alignment guide has been used for preparing a tibial surface to receive a prosthetic device as is shown in U.S. Pat. No. 4,467,801, such a planer does not provide means for orienting the abrading surface of the planer at a plurality of different angular positions which is required for preparing a femur for receiving a prosthetic device.